This invention relates to serial printers, and, more particularly, to control apparatus for serial printers.
U.S. application Ser. No. 505,105 filed in the name of Andrew Gabor on Sept. 11, 1974 for HIGH SPEED SERIAL PRINTER WITH INTERMITTENT PRINT WHEEL AND CARRIAGE MOVEMENT and assigned to the assignee of the present invention is representative of a class of high-speed serial printers employing rotatable print members, such as "daisy wheel"type print wheels. When such a printer is initially turned on, it has generally been the practice to "initialize" it. This is typically done by resetting the control logic and rotating the print member to a predetermined reference, or "home", rotational position, in order to keep track of subsequent controlled rotation of the print member. A carriage to which the print member is mounted and which is movable along a linear path, is also moved to a "home" position during printer "initialization."
In the case of the print member, initialization has generally required that the print member be rotated at a constant speed until a predetermined portion of the print member passes a predetermined reference location at which a suitable detection device is mounted. After this occurs, the print member is brought to a stop at a predetermined number of character element spaces from the point of detection. The eventual stopping location is the "home" position of the print member.
The most common ways of detecting a predetermined portion or point on the print member is by a photo-sensitive detection device or a magnetic detection device. In the first situation, a light-emitting element would direct light toward a photo-sensitive detector wherein the light would normally be blocked until an opening defined in the print member is rotated into alignment with the beam of light, allowing it to pass and strike the photo-sensitive detector. In the second situation, a megnetic element would be mounted to a predetermined portion of the print member and then detected at each pass by the magnetic detector.
At least in the case of a magnetic detector as described above, it is extremely important that the detector be precisely positioned relative to the print member so that, upon detection, the print member will be precisely stopped at its home position. If the detector is improperly positioned, the print member may stop at one or more character space positions on either side of the desired home position, thereby resulting in eventual printing errors during subsequent controlled rotation of the print member.
It would be desirable, therefore, to be able to predetermine if the detector is not properly positioned so that appropriate corrective action may be taken. It would further be desirable if the initialization procedure could be "retried" at least once following an incorrect positioning of the print member. It also would be desirable if, after a predetermined number of initialization retries have occurred with repeated incorrect print member positioning, the printer would be disabled so that the detector may be properly positioned and aligned and/or other causes of the erroneous positioning of the print member discerned and corrected.
It would additionally be desirable if, during command positioning of the print member to a desired stopping position in order to print a desired character element, such positioning process would be repeated at least once if the print member was not properly positioned the first time.